Income Taxes (Schedule of Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets
Accrued expenses and allowances	$ 16,322	$ 24,986
Inventories	4,109	11,805
Net operating loss carryforwards	33,693	48,920
Intangible Assets		14,779
Other	8,074	8,491
Subtotal	62,198	108,981
Less: valuation allowance	(20,714)	(33,427)
Total net deferred tax assets	41,484	75,554
Deferred tax liabilities
Property, plant and equipment	(344,511)	(519,977)
Intangible assets	(1,292)
Other	(1,630)	(3,952)
Total deferred tax liabilities	(347,433)	(523,929)
Net deferred tax liability	$ (305,949)	$ (448,375)